SSL devices and SSEs are increasingly in demand for many purposes because SSEs efficiently produce high-intensity, high-quality light. Mobile phones, personal digital assistants, digital cameras, MP3 players, and other portable devices use SSL devices for background illumination. Applications for SSL devices extend beyond portable electronic devices and include many types of lights, such as ceiling panels, desk lamps, refrigerator lights, table lamps, street lights, and automobile headlights.
There are several types of SSEs, such as semiconductor light-emitting diodes (LEDs), polymer light-emitting diodes (PLEDs), and organic light-emitting diodes (OLEDs). Generally, SSEs generate less heat, provide greater resistance to shock and vibration, and have longer life spans than conventional lighting devices that use filaments, plasma, or gas as sources of illumination (e.g., florescent tubes and incandescent light bulbs).
A conventional type of SSE is a “white light” LED. White light requires a mixture of wavelengths to be perceived as such by human eyes. However, LEDs typically only emit light at one particular wavelength (e.g., blue light), so LEDs must be modified to emulate white light. One conventional technique for doing so includes depositing a converter material (e.g., phosphor) on the LED. For example, as shown in FIG. 1A, a conventional SSL device 10 includes a support 2 carrying an LED 4 and a converter material 6 deposited on the LED 4. The LED 4 can include one or more light emitting components. FIG. 1B is a cross-sectional diagram of a portion of a conventional indium-gallium nitride LED 4. As shown in FIG. 1B, the LED 4 includes a substrate 12, an N-type gallium nitride (GaN) material 14, an indium gallium nitride (InGaN) material 16 (and/or GaN multiple quantum wells), and a P-type GaN material 18 on one another in series. Conventional substrates 12 are comprised of sapphire or silicon. The LED 4 can further include a first contact 20 on the P-type GaN material 18 and a second contact 22 on the N-type GaN material 14. Referring to both FIGS. 1A and 1B, in operation, the InGaN material 16 of the LED 4 emits a blue light that stimulates the converter material 6 to emit a light (e.g., a yellow light) at a desired frequency. The combination of the blue and yellow emissions appears white to human eyes if matched appropriately.
Another conventional construction of an SSL device 21 is shown in FIG. 2. The SSL device 21 has a support 23 upon which a plurality of LEDs 24 are mounted. The device 21 also includes a converter material 26, and a lens 28 formed over the LEDs 24. The converter material 26 can be formed directly on the lens 28 as shown in FIG. 2, or the converter material 26 can be formed elsewhere such that light from the LEDs 24 passes through the converter material 26.
Although LEDs produce less heat than conventional lighting devices, LEDs can produce enough heat to increase the rate at which some of the heat sensitive semiconductor and optical components deteriorate. The converter material 6, for example, deteriorates relatively rapidly at higher temperatures such that over time the converter material 6 emits light at a different frequency than the desired frequency. The combined emissions accordingly appear off-white and may reduce the color fidelity of electronic devices. The junctions between semiconductor materials that produce the light also deteriorate at higher temperatures. Therefore, it would be desirable to improve the cooling in SSEs and/or SSL devices.